Measurement of oxygen in gas mixtures



5 Sheets-Sheet l G. A. PERLEY ET AL Filed Feb. 19. y1942 June l0, 1947' G. A. PERLEY Ef AL 2,422,129.'

MEASUREMENT OF OXYGEN IN GAS MIXTURES Filed Feb. 19. 1942 5 Sheets-Sheet 2 l l INVENroRs Cl-:oncs APEnLU JAMES B. Gousnglu ATTORNEY.

June 10, 1947. G. PERLEY ET, Al. 2,422,129

' MEASUREMENT OF OXYGEN IN GAS- MIXTURES Filed Feb. 19. 1942 s sheets-shea s 4 'IIA inganna/Alu, rp

v INVENroRS Gamm: kpcmcv JAMEsGoosu-w.

- www# ATTORNEY.

Patented June 10, 1947 UNITED STATES PATENTl o 2,422,129 MEASUREMENT F OXYGEN 1N GAS MIXTUBES George A. Perley,

shalk, Philadelphia, Pa.,

Wyncote, and James B. Godassignors to Leeds and Northrup Company, Philadelphia, Fa., a corporation of Pennsylvania Application February 19, 1942, Serial No. 431,466

1 claims. (cias-232) Our invention relates to gas analysis and more particularly to systems for determining the oxygen content of gas mixture such, particularly, as those of metallurgical furnaces, boiler furnaces, cement kilns, oil refining apparatus. and

the like, all for brevity herein termed sample l gas.

vIn accordance with one aspect of our invention, a stream of the sample gas, after addition bination of hydrogen with the free oxygen of the sample gas to the substantial exclusion of reaction of the oxygen, of the hydrogen, or of both of them, with one or more other constituents,

such as carbon monoxide, carbon dioxide, methane, sulphur dioxide, of the sample gas; by

measurement of the change in the thermal conductivity of the hydrogen-sample gas mixture due to its passage through said combustion chamber, there is determined the percentage of free oxygen .in the stream of sample gas before aforesaid addition of hydrogen or equivalent.

Further in accordance with our invention, the addition of hydrogen, ammonia, or equivalent is controlled to maintain constant, in the stream of hydrogen-sample gas mixture, the ratio of hydrogen to sample gas; more particularly, the hydrogen and sample gas flow to a common mixing llne or chamber through tubes, preferably capillary, of prescribed or predetermined diameters and lengths, across each of which the pressure drop is maintained constant, or substantially so within limits suited to the desired accuracy, as by pressure-release devices comprising, preferably, liquid columns associated with constant pressure head device or devices.

Our invention further resides in the methods and apparatus hereinafter described and claimed.

For an understanding of our invention and for illustration of a system embodying it, reference is made to the accompanying drawings, in which:

Fig. 1 is a front elevational view, some parts in section and some parts broken away, of the flow system, and associated equipment, of a gasanalysis apparatus. Y

Fig. 1A schematically illustrates a modification of the system of Fig. 1.

Fig. 2 is a wiring diagram of the electrical components of a gas-analysis system including the apparatus of Fig. l and complemental measuring apparatus.

Fig. 3, on enlarged scale and in part broken away, is an elevational view of the saturator appearing in Fig. 1. y

Fig. 4 is in part a section taken on line 4 4 0f Fig. 3. i

Fig. 5 on enlarged scale and in part broken away, is an elevational view of the condenser ap'- pearing'in Fig. 1.

Fig. 6 is a plan view of Fig. 5.

Figs. 'l and 8 are front elevational views of the apparatus of Fig. 1, cabinet doors closed, with addition of traps and connections to adapt the apparatus for vacuum and pressure applications respectively.

Referring to Fig. l as exemplary of gasanalyzing apparatus embodying our invention, streams of hydrogen H (or other vapor or gas, combustible by or combinable with the oxygen or other selected component of the sample gas, equivalent to hydrogen more particularly in the sense of high amnity for the oxygen and in the sense of having thermal conductivity substantially different from that of oxygen, for example, cracked ammonia methane, or natural gas) and 4flue gas S, or other sample gas to be analyzed,

passage through device 5, in which it is saturated with water vapor, iiows as stream US through a thermal conductivity cell 8, which may be of type disclosed in United States Letters Patent Nos. 1,504,707 or 2,045,640, thence through pipe 1, to 'a furnace 8 disposed within housing 9 suitably thermally insulated from housing I0 by the layer I I of material, for example asbestos, of suitably high thermal resistance.

It is important that the walls of the reaction or combustion tube I2, located in furnace 8, with which the aforesaid gases are in contact during their combustion should be of material such as quartz, Vycor glass, Alundum or other suitable refractory material, which is substantially non-y catalytic to undesired reactions; more particularly tube I2 should not be of or contain within it a metal or alloy, such as platinum, iron, nickel, nickel-chrome, or the like, which promotes reaction of oxygen with either carbon monoxide, sulphur dioxide, or methane or which promotes realso water vapor, produced by combustion of the hydrogen added to the stream of sample gas with the free oxygen of that stream, flows through the pipe I3 to a condenser I4, or equivalent, in the lower housing I0. ,The condensate, excess water content of the comlbusted mixture,

flows from condenser Il into pipe I5 for discharge to waste, or preferably. as hereinafter detains constant the liquid level in chambers 5 and I9, a, relationship necessary for constancy of the' ratio of hydrogen to sample gas in the stream which passes through saturator to the furnace 8.

The combusted gases, now freed of their excess moisture but saturated with water vapor, pass lfrom the condenser I4v through the second thermal conductivity cell I6, similar to' cell 6, and preferably enclosed with it in the common housing I1 which serves to equalize the ambient temperature surrounding the two cells I6 and 6 so as toreduce temperature errors. The gases leaving the second cell I6 ow through pipe I8 to Waste, or preferably through chamber I9, one of the components of our arrangement for main- Lend and into which, above the1eve1qf the1iquid,

taining constant the ratio of hydrogen to sample gas. v 3

The two thermal conductivity cells 6 and I6. include resistance forming arms of a Wheatstne bridge network N, Fig. 2, whose balance point depends upon the ratio to each other of the thermal conductivities of the uncombusted and combusted gas mixtures, both saturated with water vapor at predetermined temperature,

Because these thermal conductivities are largely affected by the relative amount of hydrogen in the mixture and because the difference in hydrogen before and after combustion is a measurement of the amount of hydrogen in the sample gas, the measured change in thermal conductivity is a measure of the amount of oxygen. The following diagram discloses the reactions involved Con- Sample lilr- Cell Furnace denser Cell (s) (s) 6) (12) 14) uo a02` L aol 2aHi+a0i=2aH2o bR 6R c i bR 0:42am,

' @Hi camo whereA a, b and c are relative amounts of oxygen, agas or gases R, and hydrogen respectively; R may be or comprise any one or more of the gases carbon dioxide, methane, sulfur dioxide, nitrogen; c is not less than 2a. 1

As shown by the above diagram, the effect measured by the thermal-conductivity bridge N is the disappearance of 2a volumes of hydrogen; the volume b of gas or gases R goes through both thermal conductivity cells unchanged in magnitude, as does also the excess hydrogen. l,If R were allowedA because of catalytic action to react with lthe oxygen, or the hydrogen, or both,l

there would be substantial and indeterminate error in the measurement, Because of the reduction of volume incident to combustion, the percentage of all constituents is proportionally greater in thermal conductivity cell I6 butthisis taken into account in the calibration of the 4 I In our preferred arrangement for maintaining substantially constant the ratio of hydrogen to 4sample gas, there are provided the capillary tubes 2| and 20, included in the supply lines I and 2 for the hydrogen and sample gas respectively, and the drops inpressure across these capillary tubes are maintained equal to the same xed magnitude or to suitably different fixed magnitudes.

More specifically, pipe I, on the up-stream side of the capillary 2| is provided with a branch or tap 22 having an opening suitably below the level of liquid within chamber I9 closed at its upperl there flows through pipe I8 the combusted gases from cell I6. The exhaust or waste pipe 23 extending from chamber I9 above the surface of the liquid extends outside of housing I0 where it may be connected to a source of pressure yequal to,4

above, or below atmospheric pressure, depending upon the system from which the stream of sample gas S is Withdrawn.

It will therefore be understood that hydrogen bubbles upwardly in chamber I9 from pipe 22 at whatever -rate is required to maintain constant flow of hydrogenthrough pipe I at a rate which is a function of the distance D from the surface of the liquid in regulator I9 to the level of the opening in pipe 22; in other words,- the difference y between pressure PI on the upstream sideI of capillary 2| and the pressure P2 in chamber I9 above the liquid is maintained equal to the pressure due to the aforesaid liquid head D.

Similarly to regulate the pressure effecting flow of sample gas through capillary 28, the bleeder pipe 26 is connected to pipe 2 on the up-stream side of the capillary 20 and extends therefromto below the level of liquid in chamber I9, or similar bubbler chamber connected thereto. Accordingly the pressure P4 on the up-stream side of thev capillary 20 is maintained atv constant magnitude determined by 'the height DI of liquid from the surface of liquid in I9 to the opening in pipe 26. As pressure P4 tends to rise, more and more of the sample gas is diverted from pipe I and bubbles from pipe 26 through chamber I9 and thence to waste through pipe 23.

Beyond the capillary tubes 20 and 2|, the two streams merge in a common pipe 3 connected to the bottom of saturator 5 which, Fig. 3, comprises three concentric tubes 26A, 21B and 30. The innermost tube 26A' and intermediate tubev 21B are joined at the lower ends, the orice 28 providing communication between them. The intermediate tube 21B and outer tube 30 are joined at their lower ends, the orifice 29 providing communication between them. The inlet pipe 3 of the saturator communicates with inner tube 26A through the pair of orices |28, |29.

measuring apparatus whose scale or chart may,`

assuming the ratio of hydrogen to sample gas is maintained constant, Abe marked for direct reading of percentage of free oxygenvin the sample stream S.

'I'he joint response of cells 6 and I6 is very sensitive to changes in the percentage of hydrogen added to the stream S because an increase, for

The liquid in the saturator may, in dependence upon the nature of composition of the .combustible gas added to the sample gas, be the same as or different from the liquid in chamber I9; in the specific example discussed, it may be water,

The gas mixture passing through these orifices |28, |29 form bubbles at the lower end of tube 26A which in rising through the tube are saturated with water vapor. The upper end of tube 21B is enlarged to form bulb 35, in which any large drops of water are allowed to fall back instead of passing through the ports 34 into the chamber immediately above bulb 35 in effect a continuation of tube 21B; preferably in this` chamber is disposed a quantity of glass beads 33 (Fig, 1) or equivalent filter which trap any free moisture or mist which upon' collection trickles back through ports 34 downwardly'into and through bulb 35.

The level of liquid in the chamber defined by tubes 21B and 39 is maintained at the same level as liquid in chamber I9; in the particular system shown in Fig. 1 in which the liquids are of the same composition the pipe 3| connects to chamber I9 below the liquid levels; the spaceabove the liquid level of the saturator is, by connection 25 and pipe 23, in communicationvwith the space above the liquid level of chamber I9.

For constant rate of ilow ofthe sample-hydrogen mixture, 4the rate of bubbling through, pipe 28A ofthe saturator is constant, the back pressure produced by liquid in the tube is constant, andthe pressure drops, including those in the capillary tubes and 2l, are constant. There is therefore maintained that constancy of the ratio of hydrogen to sample gas required to ensure the measurement of change in thermal conductivity of the mixture shall be accurately indicative of the amount or percentage of oxygen in the sample gas.

In the particular arrangement shown, the capillary 20 is 'I inches long and of .025 inch inside diameter and capillary 2lv is 3 inches long and of .012 inch inside diameter.

'I'he water in the saturator 5 and the regulator device I9 maybe supplied through pipe 3I by reservoir 21 and condensate from condenser I4, all interconnected as shown inFig. l; theconnection from the condenser to the reservoir avoids back pressure otherwise possible because of collection of water in the` gas line system. Reservoir 21 serves to maintain constant the levels of liquid in chambers I9, 5 and I6 by supplyv ing liquid whenever the liquid level in chambers I9, 5 and I8 becomes too low by admitting air from .atmosphere through openings 23a and 21a into chamber 21 closed at its top by stopper 21s, thereby permitting liquid to flow vfrom 2'I through 3I again to raise the liquid level in chambers I9, 5 and I6 to the level of opening 21a; in case the level of liquid in these chambers, becomes higher than that of reservoir outlet 21a, the excess escapes through pipe 3l and outlet 21a to waste outlet 23a until the level .of liquid in chambers I9, 5 and IS returns to the level of opening 21a.

By provision of the-pressure-controlling arrangement described, or its equivalent, the rate of flow of gas to and through the furnace 8 is maintained constant. This is of importance because itI is therefore possible to use a tube I2 of such reduced cross-sectional area that the velocity of gas through the combustion chamber is so high there is not suilioient time for occurrence of relatively slow and undesired gas reactions, such as the water gas reaction, which would cause appreciable errors.

We have found that in almeasuring apparatus having a range from 0 to l0 percent oxygen in flue gas and with a gas ow of 150 cubic centimeters per minute, the tu-be I2 may have a diameter as small as l/s" or as large as 1/4 if the heated portion is 4" long and is operated at temperatures between 650 C. and 1000 C. The velocity of the sample-hydrogen mixture through the combustion zone accordingly ranges from about .450 centimeters per minute to about 1800 centimeters per minute; which velocity serves to prevent reaction of either the oxygen or hydrogen with the other components of the samplehydrogen mixture; aforesaid velocity is sufficient t0 prevent also aforesaid water gas reaction; fur- 6 thermore aforesaid velocity is nevertheless not too high to interfere with or prevent complete combustion of the oxygen and hydrogen of the mixture passing through the combustion zone.

The iilter 32 interposed in supply line 2 of the sample gas comprises a housing of Pyrex glass, or other suitable material, containing a filler of asbestos wool, or like lter material suited to remove ash, dust, soot, or other solid contaminant from the gas before it reaches the capillary tubev 2,0. The stopper 32a of rubber or other suitable c material 'is provided for convenient replacement of the charge of filter material.

All fixed parts of the saturator are preferably oi.' Pyrex glass; the stopper 38 is provided to facilitate draining of the condenser I4 and saturator 5. l

The condenser I4 is so designed that its heat capacity is or can be made substantially equal to the heat capacity of saturator 5. Consequently any smallgvariations of temperature of the atmosphere Within cabinet I0 have no ap.

. preciable effect because of substantial equality of the variations in water vapor content of gases US and CS leaving saturator 5 and condenser I4 respectively. Liquid for determining the thermal capacity of condenser I4 may be introduced into chamber 31 thereof through snout 40 normally closed by stopper 4I. 1 There is no passage connecting chamber 31 to any of the tubes I3, I6 or I5 within the condenser. y

In the arrangement shown in Fig. 1, the water vapor concentration in the gas mixture before and` after combustion is maintained constant by maintaining condenser I4 and tubes 'I and I3 at temperatures equal to or above the temperature of the saturator by their disposition within housing I0, Whose temperature is maintained constant, as by thermostatic control, and suitably thermally insulated from the furnace cabinet 9. The thermal shields 38,. 39 protect the tubes 'I and I3 from currents of relatively colder stratified air in the lower part of cabinet 9.

The'combustion tube I2 of the furnace is sur- ,f

rounded by a pairof refractory `supports or blocks in which are embedded the heating coil windings 42, 43 of Chromel, or other suitable resistance conductor, for maintaining the combustion tube at suitably high temperature,n for example above 600 C. and preferably between 650 and 1000o C. The tube temperature may be measured by a thermo-couple 44 suitably fas.- tened to the outside of tube I2 near its midpoint. The thermal insulation about the refractory block and within the metal outer casing 45 of the furnace preferably. consists of molded Sil-O-Cel blocks.

`To ensure the combustion reaction is confined to the Afurnace and does not extend into system components in chamber I0, there are provided in thel gas lines 1 and I3, within chamber 9, the

' diameter.

capillaries 46, 41 which, for example, may be about 1 inch long and of 0.6 millimeter internal The cabinet I0 is thermally insulated, as by a lining of sheet asbestos or the like and its internal temperature maintained substantially constant at suitable magnitude, for example 120 C., by the electric heaters 86, 81, Fig. '2, the energization of either or both of which is controlled by thermostat 48. The thermometer 49 for indicating the internal .cabinet temperature is visible through window 50, Figs. '1 and 8, in the door 5I. `Window 50 is of safety glass and a side of the cabinet is provided with a heavy paper blow-out; these provisions avoid damage in event I leakage of hydrogen causes a minor explosion inside of the cabinet I0.

For either pressure lor -vacuum sampling applications,y a 'trapshould be included in the exhaust line 23.and the exhaust line so disposed that condensed water drains to the trap or outlet and does not produce a variable back pressure. lWhen thel supply of sample gas S is about or below atmospheric pressure, the trap 52. Fig. 7, should extend at least-about 40 inches below connection of exhaust line 23 thereto and theexhaust line is connected, preferably through a capillary tube 53. to a vacuum pump, aspirator, or the like. f n y Y When the supply of sample gas is suillciently above atmospheric pressure, the trap. l, Fig. 8, need extend only about 6 inches below connection of exhaustv line 23 thereto 'and its upper end` directly, or through an extension oi exhaust line 23, is open to atmosphere. In-both cases, it

is desirable to connect a trap 65 to the line 2 of sample gas to remove any liquid present in the gas stream before it enters cabinet I0.,

Referring to Fig. 2, the heaters 42, 43 of the furnace and heaters 66, 81 for cabinet I0 may be energized from any suitable source oi.' current. f

for example source E of 110 volt, 60 cycle current. The bridge network N including the thermal conductivity cells 6 and |6 andthe other resistors O, may be energized from that same source E, through a suitable step-down transformer 56, about to l ratio, or from any other suitable source of direct or alternating current.

In the particular system shown, the imbalance of the network N is measured by an alternating current potentiometer network P whose components may be disposedin housing H. v l Between the coniugate points X and Y oi.' network N are connected in series the fixed resistance 51 and the voltage-dividing resistance 58 whosev contact 59 is manually adjustable to change the range of the measuring system. For use in boiler furnace installations, a full scale range of 0 to 10% oxygen is suitable; in other industrial installations, arange of 0 to 2% or 0 to 4% oxygen may be more desirable because of corresponding expansion of the scale oi' the associated indicating or recording apparatus.

The moving coil 60 of galvanometer G is normally connected between the contact 59 of the range-setting resistance 58 and the adjustable contact 6l of resistance 62 connected in shunt tothe main potentiometer slidewire 63. Contact 6i is manually adjustable to correct for shift in zero of the measiu'ing system due, for example, to variation in the percentage ci oxygen present in the tank hydrogen used as aconvenient source of supply. 'I'he usual tank hydrogen contains about 0.2% oxygen .but the concentration may vary to such extent fromthat value that except for compensation by adjustment of resistance 62 the error in measurement of free oxygen in sample S would be intolerably large. With the arrangement shown, the totalerror due `to all causes including temperature changes and line voltage variations isnot more than about .5 percent of full scale.

To minimize the effect oi' line voltage ,variations, a voltage regulator oi.' any suitable type may be connectedl between the power line and the transformers 65, 66 which Supply current to network P and to eld winding- 61 of the galvanometer G.

To measure the percentage of oxygen in the f rator 5 may be .replaced by a capillary tube orl sample gas supplied to the apparatus in cabinet I0, the .contact 68 is adiustedrelative to the potentiometer slidewire 63, either manually. or preferably automatically as by mechanical relay mechanism such as shown in Squibb Patent No.

1,935,732, until there is null deection of galvanometer G. The percentage of oxygen may then be read directly from a scale associated with the movablevelement 63 (or 66) of the potentiomv handvposition, transformer 65 is de-energizedl and the movable coil of 'the galvanometer is transferred from connection with network N to connection withresistor 12 for check of the electrical and mechanical zero of the galvanometer. To check the `zero and the range of themeasuring apparatus. it is preferable to substitute alternately for the sample gas S (with yswtchis in right-handposition) two gas mixtures, one preferably of lowy oxygen content. whose oxygen contents have been determined with an Orsat apparatus. The .zero of the system may be resetto compensate for any free oxygen, as an impurity, in the hydrogen supplied from a particular tank or reservoir. f l

In installations where speed of operation is of greater importance than high precision, Isatuequivalent having the same resistance to flow as the saturator; if such substitution is madeno readjustments are needed in the system. A1- ternatively, the saturator may be eliminated without such substitution of a capillary, and a compensation eiected by readjustment ofl contact 59 on voltage divider 58. v

The speed of response y can be increased by substituting for cell 6, traversed by the uncombusted mixture, a sealed cell containing a reference gas, such as a hydrogen-sample gas mixture, or a iixed resistor havingk the same resisttolerated if the cabinet temperature is accurately regulated. Ineach of these cases, the measure-- ment is of the change. in thermal conductivity of the gas mixture due to removal of hydrogen by combustion; in the -flrst case as above described,

the reference standard of thermal conductivity' is the uncombusted mixture itself.

Also in the interest of greater speed oi' response, the thermal-now type of cell illustrated in Fig. 1 may be replaced by one of the directflow type in which the main gas stream itself sweeps over the cell resistor.

When in' substitution for, or as a source of,

hydrogen,v the ga-s or vapor supplied to pipe I for mixture with the sample gas S is ammonia, the liquid in the flow-regulating system must be non-aqueous; it may be an oil which, unlike water, has insubstantial power of absorption of ammonia gas.4 In such modication, the saturator 5 is omitted and condenser il' may be omitted. Cracking or dissociation of the amnionia is effected within the combustion chamber l2 and the hydrogen so'releascdv immediately combines with the oxygen of the mixture. The

, 9 i diagram below indicates the reactions; the symbols a. b, c and R have the same significance as in the preceding diagram.

Sample Furnace Cell a 20H: 10|v i 20H20 24H2() I bR bR c H c/2Na (3/2c-2a)Hz (3c must be greater than 4a.)

Again it appears the principal eiIect measured is the change in thermal conductivity due to disappearance oi' ,2a volumes of hydrogen gas from the combusted mixture. n

When the sample gas includes sulfur, free or in combination, it is not practical to omit the saturator E and condenser III, for, unless the gas mixture is saturated, a iilm oi' sulfur forms on the insides o! the tubes and cells traversed by the gas-mixture. Notwithstanding need for saturation of th'e mixture with water, ammonia may nevertheless be-used as the source o1' hydrogen provided itis cracked or dissociated suit ably in advance of the saturator 5.

In the particular arrangement lshown in Fig.

1A, the precracking of the'ammonia is effected by the same furnace 8 used for effecting combustion of the hydrogen component oi' the ammonia with the oxygen of the gas sample; precracking may of course be effected within a furnace separate and distinct from furnace 8. Inasmuch as in Fig. 1A the cracking of the ammonia is effected in advance of chamber I9 as well, the liquid in chamber I9 may be water, or`

other liquid in which uncracked ammonia is highly soluble, because neither the hydrogen nor 'the nitrogen resulting .from dissociation oi the ammonia is to appreciable extent soluble therein. In general, any liquid may be used for the regulator I9 unless it dissolves or reacts with one or both oi' the combustible and sample gases.

Use of ammonia instead of tank hydrogen is preferable because it is far less explosive, its distinctive odor immediately warns of leakage,

and it is a relatively cheaper and less bulky source of hydrogen.

The reactions involved when the ammonia is pre-cracked, as in Fig. 1A, appear in the following diagram in which the symbols ua, b, c and R have the same signiilcance as in the preceding diagrams. A

From this diagram it again appears the principal eiect measured is the disappearanceof 2a" volumes of hydrogen gas which causes marked change in the thermal conductivity` of the mix,

ture denitely related to the percentage of oxy- Een in the original sample.

a gas mixture, a vapor, mixture or vapors or a mixture of one or moregases and vapor, and the term hydrogen comprehends equivalent gases and vapors which are combustible by or combine with the oxygen or other selected component ofthe sample gas.

We disclaim use or presence in the reaction or combustion chamber I2 of an electric or other heater, a protecting tube of nickel or other metal, a metallic mirror, or any other metallic or catalytic substance.

What we claim is:

1. Apparatus for analyzing a gas for its oxygen content comprising a refractory externally heated non-metallic combustion chamber, a gas sample conduit and a conduit for a combustible gas uniting andI delivering into a second chamber at a low level therein,"said. second chamber being arranged to contain water to a higher level through which the gas ascends,a thermal conductivity determination cell, a conduit connecting the upper portion of said second cham ber 'with said. cell, electrical means for measuring an electrical effect ,varying with the ther. mal conductivity of the gas passing through said cell, a conduit connecting said cell and said combustion chamber, a condenser, a conduit connecting said combustion chamber with said condenser, a second conductivity cell, a. conduit connecting said condenser with said second cell, electrical means for measuring an electrical effect varying with the thermal conductivity of the gas passing through said second cell, and means arranged to compare the magnitudes voi' said electrical eiects.

2. Apparatus for analyzing a gas for its oxygen content comprising capillary tubes for respectively conducting a gas sample and a combustible gas into mixturek with each other, said capillary tubes uniting into a single conduit, a saturator to which said single conduit connects and adapted to contain water for saturation of said mixture, a thermal conductivity determination cell, a refractory externally heated nonmetallic combustion chamber, a conduit ccnnecting said saturator Yto said cell anda conduit connecting said cell with said combustion chamber, a second thermal conductivity cell, a condenser, a conduit connecting the discharge of said combustion chamber with said condenser, a

conduit connecting said condenser with said second cel1a pressure-regulating system comprising a closed chamber adapted to contain liquid, bleeder connections from the upstream sides of aforesaid capillary tubes to points below the normal level ofthe liquid in saidclosed chamber, a

urated resultant mixture through a refractory externally heated non-metallic combustion chamber` and thereby e'ectlng combustion 'of hydrogen of said resultant mixture, effecting saturation of the combusted mixture with water, and measuring the changes in the thermal conductivities of the saturated mixture before and after passage through said combustion chamber.

4. A method of analyzing a gas mixture comprising oxygen and one or more otherlgases, such as carbon monoxide, carbon dioxide, sulphur dioxide or methane, which comprises mixing an water, and measuring the changevin thermal con- ,ductivities of the saturated gas mixture before entry into and after discharge from said combustion chamber.

7. A method of determining the oxygen content of a gas mixture comprising one or more other gases, such as carbon monoxide, carbon di.v oxide, sulphur dioxide or methane, which comprises mixing with a sample of the gas mixture excess of combustible gas with a sampley of aforesaid mixture, passing the resultant mixture o! sample gas and added combustible gas through a non-metallic combustion chamber, raisingv the mixture, while traversing said combustion chamber, by heat generated externally thereof, to a temperature within a range from about 650 C. to

about 1000 C. to effect selective combustion of the oxygen of the sample gas mixture with the added combustible gas, and measuring the change in the thermal conductivity of the gases prior and subsequent to aforesaid selective combustion.

5. A method of analyzing a gas mixture com-- prisingoxygen and one or more other gases, such as carbon monoxide, carbon dioxide, sulphur dioxide or methane, which comprises mixing a combustible gas with a sample of the gas mixture, subjecting the resultant mixture, while traversing a non-metallic externally heated combustion chamber at a velocity of from about 450 to about 1800 centimeters per minute, to a temperature within the range from about 650 C. to about 1000 C., and measuring the change in the thermal conductivity of the gas mixture on entering and discharge from said combustion chamber.

6. A method of analyzing a gas mixture com-v V prising oxygen and one or more other gases, such as carbon monoxide, carbon dioxide, sulphur di-` oxide or methane, which comprises mixinga com` bustible gas with a sample of the aforesaid gas mixture, saturating the resultant mixture with water, subjecting the saturated mixtureI while traversing a non-metallic externally heated 'combustion chamber, at a velocity of' from about 450 to about 1800 centimeters per minute, to a temperature within the range from about 650 C. to about 1000 C., saturating the gas mixture discharge'd from said combustion chamber with a gas to be combusted by the oxygen of the sample, saturating the resultant mixture with water, subjecting the saturated mixture, while traversing an externally heated lnon-metallic combustion chamber, at a velocity of from'about 450 to about 1800 centimeters per minute, to a 'temperature within the range from about 650 C. to about 1000 C., causing the mixture discharged from said combustion chamber to be saturated with but devoid of excess water, and measuring the Ychange lin thermal conductivities of the saturated mixtures before entering and after discharge from said combustion chamber.

GEORGE A. PERLEY. JAMES B. GODSHALK.

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